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• monovalent

• monoenergetic

• bivalent (alternative, parallel)

• bivalent regenerative

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Evaporator output Q₀ (kW_th) = Heating capacity Q_C. (kW_th) - electrical power consumption of the compressor P_el (kW_el)

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The brine throughput specified in the device information of the heat pump corresponds to a temperature spread of the heat source of approx. 3 K. In addition to the volume flow, the pressure losses in the brine circuit system and the technical data of the pump manufacturer must be taken into account. In doing so, pressure losses in pipelines, internals and heat exchangers connected in series must be added.

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• Cleaning the dirt filter in the heat pump's brine circuit

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The building should be dried out with special, on-site devices. If the heating output of the heat pump is limited and the building dries out in autumn or winter, it is advisable to install an additional electric heating element, especially with brine / water heat pumps, to compensate for the increased heat demand. This should only be activated in the first heating period depending on the brine flow temperature (approx. 0 ° C).

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A mixture of water and an anti-freeze agent is used as the heat transfer medium in order to achieve a lower freezing point. Ethanediol (ethylene glycol) is used as an antifreeze in the majority of plants in Germany, Austria and Switzerland.

The use of pure monoethylene glycol is therefore recommended if it can be ensured that there is no permanent supply of oxygen during operation due to a closed brine circuit (e.g. AFN 824, AFN 825).

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Table 3.1: Approved antifreeze agents recommended by Dimplex

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• "Thermera", which is made on the basis of betaine and is not without controversy from an environmental point of view.

• "Tyfo special without corrosion protection inhibitors", as this antifreeze attacks non-ferrous metals such as copper.

• "Tyfo special with corrosion protection inhibitors", as this is not officially approved by our suppliers and is so aggressive that it leads to corrosion on the sheet metal cladding in the event of leaks.

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Pressure protection
If only heat is extracted from the ground, brine temperatures between approx. 5 ° C and approx. +20 ° C can occur. Due to these temperature fluctuations, there is a change in volume of approx. 0.8 to 1% of the system volume. In order to keep the operating pressure constant, an expansion vessel with a pre-pressure of 0.5 bar and a maximum operating pressure of 3 bar must be used.

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• Mix the required antifreeze-water concentration in an external container

• Check the previously mixed antifreeze / water concentration with an antifreeze tester for ethylene glycol

• Filling the brine circuit (max. 2.5 bar)

• Vent the system (install microbubble separator)

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Other materials
When using other materials such as copper, brass or stainless steel in the brine circuit, the corrosion resistance of the materials must be checked. Corrosion can also occur due to condensation on pipes that are not or inadequately insulated in the brine circuit.

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Fig. 3.3: Parallel connection of brine / water heat pumps

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The coupling to the earth's surface is decisive for the performance of geothermal collectors, as they are affected by heat input from outside air, solar radiation and precipitation in the warmer months
be regenerated. The following design guidelines and application limits therefore apply exclusively to geothermal collectors that are not covered or sealed and that are covered by the natural soil. The heat inflow from the earth's interior is less than 0.1 W / m² and therefore negligible.

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• In individual cases, geothermal collectors are subject to notification or approval from the lower water authority.

• Building over the geothermal collector is not permitted. The terrain surface above a collector system must not be sealed, as this impairs regeneration.

• A deeply rooted vegetation over a collector is to be avoided. In the worst case, the vegetation delay over a collector is around two weeks.

• The following minimum clearances and standard dimensions are recommended:
  - between collector and buildings: 1.2 m
  - Lines leading between collector and water: 1.5 m
  - between the collector and the property line: 1 m
  - Installation depth of the collector: see section below
  - Installation distance of the collector pipes: see section below

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In cold regions, the ground temperatures at a depth of 1 m can reach the freezing point even without using heat. At a depth of 2 m, the minimum temperature is approx. 5 ° C. This temperature rises with increasing depth, but the heat flow from the earth's surface decreases. A thawing of the icing in spring is not guaranteed if it is laid too deeply. Therefore, the laying depth should be approx. 0.2 to 0.3 m below the maximum frost limit. In most regions of Germany this is 1.0 to 1.5 m.

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• The longer the maximum duration of the frost period, the greater the laying distance and the required area.

• In the case of poor heat conduction of the floor (e.g. sand), the installation distance must be reduced for the same installation area and thus the total pipe length increased.

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• Cooling capacity of the heat pump

• Soil type and moisture content of the soil and climatic region

• Maximum length of the frost period

• Annual full hours of use

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• If the brine distributors are installed inside a building, they and all pipelines in the house and through the house wall must be insulated so that they are vapor-diffusion-proof in order to prevent condensation.

• For each collector circuit, the collector pipe should not be longer than 100 m, with probe pipes DN 32 a maximum depth of 80 m should not be exceeded - note pressure loss.

• Hand-tighten all screw connections on the brine collector and distributor. Then tighten with a tightening torque of 60 to a maximum of 70 Nm. Do not damage the union nuts when tightening.

• Coat the union nut between the brine distributor or brine collector and the ball valve (compression fitting) with a grease paste to prevent moisture from penetrating.

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• The individual brine circuits must be hydraulically balanced with one another. Ideally, collector pipe coils of the same length and material properties are laid (Tichelmann principle). Bar regulating valves (e.g. taco-setter) in the individual brine circuits mean an additional pressure loss and thus higher power consumption by the circulation pump in the heat source circuit.

• Each brine circuit must be provided with at least one shut-off valve.

• The brine circles must all be of the same length in order to ensure an even flow and extraction capacity of the brine circles.

• The geothermal collectors should be installed a few months before the heating season if possible so that the ground can settle.

• The minimum bending radii of the pipes according to the manufacturer's specifications must be observed.

• The filling and venting device must be installed at the highest point on the site.

• When laying the brine lines and the intermediate circuit, it must be ensured that no air pockets form.

• All brine pipes (flow and return) in the house and through the house wall must be insulated so that they are vapor diffusion-proof in order to avoid heat and cold losses and to prevent condensation.

• All pipes carrying brine must be made of corrosion-resistant material.

• Brine distributors and return collectors should be installed outside the house.

• When installing the brine circulating pump of the heat source system, the temperature ranges of the pump in the installation instructions must be observed. The position of the pump head must be set so that no condensate can flow into the connection box. If it is installed in a building, it must be insulated so that it is vapor diffusion-proof in order to prevent condensation and ice formation. In addition, soundproofing measures may be necessary.

• The laying distance between pipes carrying brine and water pipes, canals and buildings should be at least 1.2 - 1.5 m in order to avoid frost damage. If this installation distance cannot be maintained for structural reasons, the pipes must be adequately insulated in this area.

• Geothermal collectors must not be built over and the surface must not be sealed.

• The large ventilator with micro-bubble separator should be located at the highest point of the brine circuit. The brine accessories can be installed both inside and outside the building.

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Fig. 3.9: Structure of the brine circuit feed line including fittings

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• PE pipe (brine circles): pipe DIN 8074 32 x 2.9 mm - PE 100 (PN 12.5)

• PE supply pipe between heat pump and brine circuit according to DIN 8074:

• Nominal pressure PN 12.5 (12.5 bar)

• specific extraction capacity of the soil approx. 25 W / m² at a laying distance of 0.8 m

• Brine concentration min. 25% to max. 30% antifreeze (glycol-based)

• Pressure expansion vessel: 0.5 - 0.7 bar pre-pressure

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The required quantities of antifreeze in Tab.3.2 refer to the specified wall thicknesses. With thinner walls, the amount of water and frost protection must be increased and adjusted so that the minimum brine concentration of 25% by volume is achieved.

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Earth temperatures
The earth temperature is 10 ° C all year round from a depth of approx. 15 m.

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Geothermal probes are generally designed by planning offices for geothermal energy. An approximate determination of geothermal probes, even in the small power range, is not permitted. This is necessary because the extraction rate depends on the nature of the soil and the water-bearing layers. These factors can only be clarified on site by an executing company.

The long-term, computational simulation of load profiles enables long-term effects to be recognized and taken into account in the project planning. For example, using the probe in summer for passive cooling has a positive effect on regeneration.

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• between probe and buildings: 2 m (the statics must not be impaired).

• between the probe and the pipes carrying water: 2 m to 3 m (differently regulated locally)

• between connecting pipes and pipes carrying water: 1.5 m

• Distances to the neighboring property vary from country to country (recommendation VDI 4640 Part 2, distance between geothermal probes 6 m, distance to the neighbor's probe 10 m, exceptions are possible in coordination with the neighbors).

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Fig. 3.12: Probe cross-section of a double U probe with a filling pipe

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Tab.3.7: Overview table of the brine accessory packages for 2-compressor brine / water heat pumps

Brine deficiency and leakage
In order to detect a possible lack of fluid or a leak in the brine circuit or to meet official requirements, the "low-pressure pressostat brine", available as a special accessory, can be installed in the brine circuit. Heat pump locks.

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Fig.3.13: Low pressure pressostat brine (structure and interconnection)

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• Pressure loss at the specified brine throughput for the design of the brine circulating pump

• Possible influences on the vegetation

• Installation regulations

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The external stainless steel heat exchanger makes it possible to use the groundwater heat source even in areas with heavier water pollution. In areas with a year-round water temperature below 13 ° C, no water analysis for corrosion is necessary.

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The maximum permissible flow temperatures on the heat source side of a brine / water heat pump are 25 ° C. To prevent the heat pump from switching off due to excessive brine inlet temperatures, there are various options that are described in the following chapter.

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If the temperature of the heat source fluctuates, the use of a brine / water heat pump is recommended, as minimum brine outlet temperatures of -9 ° C are possible here. In comparison, water / water heat pumps switch off at a minimum water outlet temperature of 4 ° C. The maximum brine inlet temperature for both brine / water and water / water heat pumps is 25 ° C. Exceeding or falling below the application limits can be prevented in various ways.

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Variant 2 - heat pump with buffer storage in the brine circuit
Variant 2 provides for the use of a buffer storage tank in the brine circuit (see Fig. 3.16 on p. 22). The buffer storage tank is loaded by means of an external control system via pump P1. From a minimum temperature of 3 ° C in the buffer tank, the pump is activated and loads it. Pump P1 switches off when the temperature reaches a maximum of 24 ° C. The heat source pump (primary circulation pump M11) in the brine circuit is controlled by the heat pump manager. If a temperature of 3 ° C below or a temperature of 25 ° C is reached on the temperature sensor (R6), the heat pump manager switches off the heat source pump. The brine circuit must be filled with glycol with at least 25% by volume.

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Fig.3.16: Heat pump with buffer storage in the brine circuit

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• The design of the absorber surface should in principle be based on the specified night performance of the absorber.

• At air temperatures above 0 ° C, rain, condensation or snow can freeze on the absorber surface at low brine temperatures, which negatively affects the flow of heat.

• Monovalent operation is only possible in combination with the use of geothermal energy.

• With solar energy gains in the transition period, brine temperatures of 50 ° C and more occur, which exceed the application range of the heat pump.

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